3. Delegates and events: closure, C#

3. Delegates and events: closure

//3. Delegates and events: closure

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {

delegate bool TestPointer(int a);   
        static event TestPointer SomeEvent; 
        
        public static void Main(string[] args)
        {
            Subscribe();
            // a that was local to Subscribe() is gone.
            //However when we fire event it is printed just fine.
            SomeEvent(0);
            
            //This is achieved by compiler which constructs special class that holds copy of all the variables that are referenced in the event handler.
            //This is called closure and allows us to use anything that was available at the time of subscription, no matter when it will actually be called.
            //If we use complex types than closure classes will keep references to them, so we can use them as well.
        }
        
        public static void Subscribe()
        {
            int a = 5;    //a is local variable to this method and will be removed from memory as soon as this method is over
            SomeEvent += f =>
            {
                Console.WriteLine("a is " + a); //we use a, when original a is not there anymore!
                return true;
            };
        }
    }
}


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